Q. No.An AC voltage source is connected to a series \(LCR\) circuit. When \(L\) is removed from the circuit, the phase difference between current and voltage is \(\dfrac{\pi}{3}\). If \(C\) is instead removed from the circuit, the phase difference is again \(\dfrac{\pi}{3}\) between current and voltage. The power factor of the circuit is:
1. \(0.5\)
2. \(1.0\)
3. \(-1.0\)
4. zero
1. \(0.5\)
2. \(1.0\)
3. \(-1.0\)
4. zero
| 1. | \(2.05~\text A\) | 2. | \(2.5~\text A\) |
| 3. | \(25.1~\text A\) | 4. | \(1.7~\text A\) |
A light bulb and an inductor coil are connected to an AC source through a key as shown in the figure below. The key is closed and after some time an iron rod is inserted into the interior of the inductor. The glow of the light bulb:
| 1. | decreases | 2. | remains unchanged |
| 3. | will fluctuate | 4. | increases |
A circuit when connected to an AC source of \(12~\text{V}\) gives a current of \(0.2~\text{A}\). The same circuit when connected to a DC source of \(12~\text{V}\), gives a current of \(0.4~\text{A}\). The circuit is:
| 1. | series \({LR}\) | 2. | series \({RC}\) |
| 3. | series \({LC}\) | 4. | series \({LCR}\) |
The variation of EMF with time for four types of generators is shown in the figures. Which amongst them can be called AC voltage?
 |
 |
| (a) | (b) |
 |
 |
| (c) | (d) |
| 1. | (a) and (d) |
| 2. | (a), (b), (c), and (d) |
| 3. | (a) and (b) |
| 4. | only (a) |
A coil of inductive reactance \(31~\Omega\) has a resistance of
\(8~\Omega\). It is placed in series with a condenser of capacitive reactance \(25~\Omega\). The combination is connected to an a.c. source of
\(110~\text{V}\). The power factor of the circuit is:
1. \(0.56\)
2. \(0.64\)
3. \(0.80\)
4. \(0.33\)
The core of a transformer is laminated so that:
| 1. | energy losses due to eddy currents may be minimized |
| 2. | the weight of the transformer may be reduced |
| 3. | rusting of the core may be prevented |
| 4. | the ratio of voltage in primary and secondary may be increased |
A transistor-oscillator using a resonant circuit with an inductance \(L\) (of negligible resistance) and a capacitance \(C\) has a frequency \(f.\) If \(L\) is doubled and \(C\) is changed to \(4C,\) the frequency will be:
1. \(f/4\)
2. \(8f\)
3. \(f/2\sqrt2\)
4. \(f/2\)
A transformer is used to light a \(100~\text{W}\) and \(110~\text{V}\) lamp from a \(220~\text{V}\) main. If the main current is \(0.5~\text{A},\) the efficiency of the transformer is approximately:
1. \(30\%\)
2. \(50\%\)
3. \(90\%\)
4. \(10\%\)
What is the value of inductance L for which the current is maximum in a series LCR circuit with C = 10 μF and ω=1000 s-1?
1. 100 mH
2. 1 mH
3. cannot be calculated unless R is known
4. 10 mH
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